The Effects of Complex Terrain The Effects of Complex Terrain on Sever Landfalling Tropical on Sever Landfalling Tropical Cyclone Larry (2006) over Cyclone Larry (2006) over Northeast Australia Northeast Australia
Hamish A. Ramsay and Lance M. Leslie,2008: The Effects of Complex Terrain on Sever Landfalling Tropical Cyclone Larry (2006) over Northeast Australia, Mon. Wea. Rev., 136,4334-4354
The Overview of TC LarryThe Overview of TC Larry
Townsville
BK
BF
(Bellenden Ker; 1593 m)
(Bartle Frere; 1622 m)
Complex TerrainComplex Terrain
Date & Time Description
0600 UTC 17 March About 1500km east of Cairns
1800 UTC 17 March Category 1 TC
Morning of 18 March Severe TC
1110 UTC 19 March The wind gust reach 59 m/s
2100 UTC 19 March Making landfall
Model MM5 V. 3.7
Domain D1:27 km ; D2: 9 km ; D3: 3 km ; D4: 1 km
Levels 46 half-sigma levels, extend vertically up to 50 hPa
Microphysics Resiner Mixing – Phase ( Reisner et al. 1998)
PBL The Eta Model Mellor-Yamada scheme
RadiationRapid Radiation Transfer Model (RRTM; Mlawer et al. 1997)
ICNCEP Final Analysis (FNL) 1 。 X 1 。 resolution
BC
Cumulus Betts-Miller (1986) ,only D1 & D2
Model Setting Model Setting
8
Terrain DataTerrain DataHigh resolution terrain data with
horizontal resolution of 900m was used in D4
Mt. Bartle Frere : nature: 1622 m model: 1600 m Mt. Bellenden Ker : nature: 1593 m model: 1484
m
a. TC track and intensitya. TC track and intensity
RESULTS
The simulated TC track is in very good agreement with the observed track of TC Larry
The simulated TC with topography crossed the coast about 2 h after the observed time of Larry’s landfall
NOTOPOG TC is 18 hPa deeper than CTRL TC
SST is not different between two simulations
36h
Track & Central Pressure
b. TC structure during b. TC structure during landfalllandfall
RESULTS
Surface Wind Speed and Direction
The ‘‘surface wind’’ denotes the 10-m wind .
The TC’s tangential flow is accelerated by the orography
Surface wind of up to 38m/s are evidence on their (Mt. BK and BF) southern slopes
The surface winds on the sheltered lee sides of these mountains are significantly lower
CTRL TC have more tilting (vertical wind shear) than NOTOPOG TC
50-58 m/s
50 m/sBK
BF
77 m/s@500m
73 m/s@600m
CTRL TC
Surface Wind Speed and Direction
The maximum surface winds are located in the eastern half of the circulation over water, collocated with a maximum in low-level cyclonic vorticity and very strong gradient of EPT
50-58 m/s
50 m/sBK
BF
NOTOPOG TC
60 m/s
67 m/s@250m
82 m/s@250m
CTRL
NOTOPOG
Equivalent Potential Temperature (contour)Cyclonic vertical vorticity (sading) at 1 km NOTOPOG TC have a strong
warm core with a maximum equivalent potential temperature of 380 K ( 5K higher than the 375 K for CTRL TC )near the center of eye
CTRL TC NOTOPOG TC
Pentagonal-shaped Pentagonal-shaped eyewalleyewall
Observed Simulated (CTRL)
c. Boundary layer c. Boundary layer turbulenceturbulence
RESULTS
TKE maxima South of TC eye A narrow band west of the
eye The windward slope
The spatial distribution of the vertical shear in the lowest 100 m is in very close agreement with the spatial distribution of TKE
CTRL
CTRL
NOTOPOG
Ocean:< 80 J/kgOcean:< 80 J/kg
Land:180 J/kgLand:180 J/kg
The contour is vertical shearThe contour is vertical shear
The 50-m wind speed over the eastern slopes of Mt. BF (~1200m)is 56 m/s whereas the surface wind is only 32 m/s
Over the northern slopes of the mountain (~960m)the 50-m wind speed is only 16 m/s
Similar speedup/sheltering effects that coincide with distinct maxima and minima of TKE are also noted over and around Mt. BK father to the north
d. Influence of orography on d. Influence of orography on
TC windsTC winds
RESULTS
2100 UTC 18 MARCH 0100 UTC 19 MARCH
68 m/s
An observed westerly wind gust of 82 m/s was recorded at roughly the same location
Mt. BK50-60 m/s
e. Downslope winds in the e. Downslope winds in the Port Douglas regionPort Douglas region
RESULTS
4-8 m/s 16-20
m/s
2300 UTC 18 MARCH 0030 UTC 19 MARCH
~24 m/s
~4 m/s
Critical layers (10 km) have been shown to play an important role in the amplification of mountain waves and subsequent intensification of severe downslop windstorm (Clark and Peltier 1984)
f. Rainfallf. Rainfall
RESULTS
Chen et al. (2006) show that for TCs in the Southern Hemisphere, enhanced precipitation is favored to the right of the deep-layer environmental shear
For CTRL, analyses of the column-integration cloud liquid water content indicates maximum values occur generally in the front-left quadrant of the vortex, upstream of the heavy precipitation in the front-right /rear-right quadrants.
12-h Accumulated Rainfall
CTRL
NOTOPOG
<5 m/s wind shear
CTRLNOTOPOG
200 mm
225 mm
75-100 mm2300UTC 19
0200 UTC 20
0500 UTC 20
0000 UTC 20
0300 UTC 20
0600 UTC 20
~70-100 mm
200 mm
175 mm
In despite of the NOTOPOG TC’s intensity is greater than CTRL TC, the accumulated rainfall of NOTOPOG TC’s is less than in the CTRL TC.NOTOPOG TC have more moisture content compared with the CTRL TC
Summary (I)Summary (I)These boundary layer jets
produced strong low-level vertical wind shear (30 m /s);
The shape of this range is well-suited for generating severe downslope winds, with its steep leeside slope and gentle windward rise.
Summary (II) Summary (II) Rainfall amounts and patterns
associated with TC Larry were reproduced well by the CTRL simulation, with 3-h totals in excess of 200 mm over the steep coastal orography.
In contrast, the 3-h rainfall totals for the NOTOPOG TC were lower immediately following landfall, but increased relative to CTRL as the system moved farther inland.
Summary (III) Summary (III) Small-scale banding features
were evident in the surface wind field over land for the NOTOPOG TC, due to the interaction between the TC boundary layer flow and land surface characteristics